Since tornado websockets use python Future, the python3 kernel crash at file

/usr/local/lib/python3.7/site-packages/notebook/services/kernels/handlers.py

at the line 207

https://github.com/jupyter/notebook/blob/57db70979b677b0c47cbecfbfbc3ba5b359bc0b3/notebook/services/kernels/handlers.py#L207


if self.ws_connection is None or self.ws_connection.is_closing():

Here since self.ws_connection is a Future it does not have the member: is_closing

A fix would be to wait for the Future result (with or without a timeout) :

websocket = self.ws_connection.result()

And then check for
websocket.is_closing()

The dirty fix would be to ignore the test on is_closing

With the dirty fix the kernel run

The github repos have over 2k issue, it is hard to find if this error was already reported there.